This invention relates generally to a system and method for placing leads within a body; and more particular, relates to the use of audio signals for determining lead location and for assessing the level of tissue contact achieved by one or more devices carried on the lead.
Implantable medical electrical leads have long been employed in the fields of cardiac stimulation and monitoring. For example, leads are generally employed to deliver electrical stimulation for cardiac pacing and cardioversion/defibrillation applications. In these applications, endocardial leads are placed through a transvenous route to locate one or more sensing and/or stimulation electrodes in a desired location within a heart chamber or interconnecting vasculature. To provide effective therapy, electrodes carried at the lead distal end need to be accurately positioned at a predetermined location against the endocardium or within the myocardium. The lead distal tip is then generally affixed by a passive or active means to the tissue to maintain the desired locations.
It is often difficult to determine whether a lead has been properly positioned and adequate tissue contact has been achieved. In some instances, catheters and leads are utilized that include materials that will allow for visualization with fluoroscopy. Additionally, fluoro-visible dyes may be injected into the cardiac chambers and venous anatomy so that the chambers of the heart and the related vasculature are visible using a fluoroscopic device. This procedure, sometimes referred to as a xe2x80x9cvenogramxe2x80x9d, allows the surgeon to locate a precise site and achieve proper electrode placement when performing an implant procedure.
Although the use of fluoro visible media is viable in some instances, this process has several disadvantages. First, some patients have adverse physical reactions when exposed to the fluoro visible dye used to obtain a venogram. Moreover, obtaining the venogram exposes the patient and clinicians to radiation. Additionally, a fluoroscope of the type needed for obtaining the fluoro-visible image may not be available. Finally, obtaining the venogram adds additional steps to the implant procedure, lengthening the time required to complete the procedure and increasing the risk of infection and complications to the patient.
What is needed, therefore, is an alternative system and method for placing, and otherwise monitoring the status of, an implantable medical device within the vascular system of the body without the need to inject a fluoro visible media into the body.
The current invention provides an improved system for monitoring status of an IMD within a body. The system includes a device such as a lead, guidewire, stylet, catheter, or other IMD carrying a device such as a microphone for detecting acoustic signals in the body. The IMD is coupled to an amplifier device which, in one embodiment, may be provided by a stand-alone device or included within an external programmer. An electrical representation of the measured acoustic signal is provided by the IMD to the amplifier device so that an audible signal may be generated by the amplifier device. A trained user can utilize the pitch and other characteristics of the audible signal to determine status associated with the IMD. Because unique patterns are associated with the acoustic signals that may be measured at distinct points within the cardiovascular system, the pitch of the audible signal may be used to determine the location of the acoustic measuring device, and thus, the IMD, within the body. Other information may be gained from the audible signal, including the extent of any contact between the IMD and tissue, and/or the extent of fixation of the IMD to tissue.
In one embodiment of the invention, the amplifier device includes a processing circuit to analyze the audible signal. For example, the processing circuit may compare the sensed audible signals to stored patterns. This comparison may then be used to determine IMD status, including location and tissue contact data. The processing circuit may provide this status information to an output device such as a printer or display monitor. According to one aspect of the invention, a virtual image of the IMD within the body may be generated using the status information.
The IMD of the current invention may include a switch mechanism. This switch mechanism may be used to selectively couple signals generated by the acoustic measurement device to a connector of the IMD during an implant procedure. This switch is re-configured during normal IMD operation so that other sensing devices such as electrodes are coupled to the connector. Use of this type of switching mechanism allows a standard connector, or alternatively, a non-standard connector having minimal connector contacts, to be utilized by the IMD.
The IMD may further include additional physiological sensors such as pressure, temperature, flow velocity, flow acceleration, and electrical activity sensors to provide additional physiological signals measured within the cardiovascular system to the amplifier device. This data may be utilized to confirm, or to further enhance, the status data that is generated using the acoustic signals.
In one embodiment of the invention, the amplifier device is included within a second IMD such as a pacemaker, cardioverter/defibrillator, drug pump, or any other implantable medical device rather than an external device. Periodic acoustic measurements are provided by the first IMD, which may be a lead, to the second IMD. This may involve configuring an electronic switch included within the lead to make the signals available to the second IMD. These acoustic signals may then be used by the second IMD to detect dislodgement or detachment of the first IMD, or to analyze a patient""s condition. In response to the sensing of a predetermined patient condition, the second IMD may issue an alert or modify therapy delivery. The acoustic data may further be stored as trend data that may be used by a clinician in evaluating long-term patient condition. Other aspects of the current invention will become apparent to those skilled in the art from the drawings and accompanying description.